Method and apparatus for testing threaded joints and threaded members

ABSTRACT

PCT No. PCT/GB96/01958 Sec. 371 Date Feb. 28, 1998 Sec. 102(e) Date Feb. 28, 1998 PCT Filed Aug. 12, 1996 PCT Pub. No. WO97/09597 PCT Pub. Date Mar. 13, 1997A method for testing threaded joints and threaded members comprising the steps of lubricating one or both threaded members, making up a joint, subjecting the joint to a pressure differential, and attempting to detect flow through said joint, characterized in that said method includes the step of subjecting said joint to heat during the test.

This invention relates to a method and apparatus for testing threadedjoints and threaded members.

Typically, tubulars used in the construction of oil and gas wells arejoined via threaded members. It is often extremely important that thethreaded joints do not leak and it is becoming increasingly common forthreaded members, for example the pins and boxes on tubulars, andsockets for joining tubulars, to be tested (1) during production; (2)before being dispatched from a depot; and (3) as the tubular string ismade up and lowered down a well.

A wide variety of testing methods are available. In factories and depotsthe majority involve lubricating one or both threaded members, making upa dummy threaded joint, subjecting the dummy threaded joint to apressure differential, and attempting to detect flow through thethreaded joint. A similar method is used as a tubular string is made upand lowered down a well except that the final threaded joint is tested.

Lubrication is generally effected using a material which is usuallyreferred to as "dope". This is a mandatory procedure specified bytubular manufacturers. The problem which arises is that the presence ofthe dope can result in threaded joints passing tests but subsequentlyleaking. It is believed that this phenomena is caused by the dopeeffectively plugging small defects for the duration of the test which istypically from 90 to 120 seconds. If the dope is not applied then thethreads may be galled.

In a conference paper entitled "Gasdichte Gewindeverbinder Theorie undPraxis" (Gas tight screw couplings in theory and practice) delivered atClausthal-Zellerfeld University on Apr. 15, 1988 to the German Societyfor Mineral Oil Techniques and Coal Chemistry, the authors, G. Wilken,E. Eide and P. Stoffels observed that hot joints were more likely toleak than cold joints. However, the authors did not make any comments asto how their observation might be used and, indeed, commercial testingprocedures subsequently remained largely unchanged.

It is an aim of the present invention to reduce the probability of ajoint wrongly passing a test and to enable faulty joints to beidentified more rapidly than in conventional testing.

According to the present invention there is provided a method fortesting threaded joints and threaded members, which method comprises thesteps of lubricating one or both threaded members, making up a joint,subjecting said joint to a pressure differential, and attempting todetect flow through said joint, characterised in that said methodincludes the step of subjecting said joint to heat in order to reducethe viscosity of said lubricant.

The heat may be applied to the joint before, during or before and duringtesting. However, it is particularly advantageous to commence heating atthe same time as pressure is applied to the joint.

During trials a joint with a very small mechanical defect which passedconventional testing was heated during testing and promptly failed. Inanother test a joint which had failed a few seconds before the end ofconventional pressure testing was dismantled. The threaded members werecleaned and the joint remade using dope. When tested by a method inaccordance with the present invention the joint failed after just 10seconds. The joint was dismantled. The threaded member cleaned and thejoint remade using dope. The first test was repeated and, again onlyfailed a few seconds before the end of the conventional pressure test.

Heating may be effected by any suitable means. However, inductiveheating is currently favoured. Alternative methods of heating includeelectrical resistance heating, steam heating, heating with hot air orvapour, or even the application of a bag or jacket containing a hotmaterial which could be liquid, solid or gaseous.

The method of the present invention is primarily intended for testing asuccession of threaded members and accordingly the present inventionextends to repeatedly carrying out the method of the present invention,preferably at a rate of at least five and preferably at least ten testsper hour.

If desired the joint may be subjected to vibration during testing, forexample at ultrasonic frequencies.

The present invention also provides an apparatus for testing alubricated threaded joint, which apparatus comprises means for applyinga test fluid (i.e. liquid and/or gas) under pressure to one side of alubricated threaded joint, and means for detecting flow through saidlubricated threaded joint, characterised in that said apparatus furthercomprises a heater arranged to be disposed directly circumjacent saidlubricated threaded joint for heating said lubricated threaded joint toreduce the viscosity of lubricant in said lubricated threaded joint.

Preferably, said means for heating said threaded joint comprises aninduction heater.

Advantageously, said apparatus is adapted to applying said test fluidunder pressure to the inside of a joint. However, if desired, theapparatus could be adapted to apply said test fluid under pressure tothe outside of the joint.

The means for detecting flow through the threaded joint may comprise,for example a pressure gauge communicating with the pressure applied tothe joint. Leakage through the joints would be indicated by a fall inpressure. This technique would primarily be applicable for use when thetest fluid is a liquid. An alternative means for detecting flow throughthe threaded joint could comprise a gas detector or mass spectrometerwhen the test fluid is a gas.

The test fluid may comprise a liquid or a gas, nitrogen or helium beingrecommended.

For a better understanding of the present invention reference will nowbe made, by way of example, to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevation, partly in section, showing onetubular threadedly connected to another;

FIG. 2 is a view similar to FIG. 1 showing the joint being tested usingone embodiment of an internal pressure tester;

FIG. 3 is a view similar to FIG. 2 showing a different type of jointbeing tested using another embodiment of an internal pressure tester;

FIG. 4 shows a modification of the embodiment shown in FIG. 3; and

FIG. 5 is a cross-section showing a joint being tested by an externalpressure tester during the running of casing into a well.

Referring to FIG. 1, there is shown a tubular which is generallyidentified by the reference numeral 100. The tubular 100 is providedwith a threaded pin 101.

There are a large number of different designs of pins. Some are designedto seal on first shoulder 102, some on second shoulder 103, and some ona combination of the first shoulder 102 and the second shoulder 103.Some have a centre shoulder 104, and some rely on interference betweenthe threads 105.

In all cases the threaded pin 101 has to be correctly formed to sealproperly.

In a factory the threaded pin 101 is tested by applying dope to thethreaded pin 101 and screwing it into a threaded box 106 on a shorttubular 107 (FIG. 2) which is secured in a vice (not shown).

The joint 108 is then tested to see whether any fluid can pass acrossthe joint 108. In order to test the joint 108 an internal pressuretester 109 is inserted through the short tubular 107 and positioned asshown in FIG. 2.

Seals 110 are urged radially outwardly by introducing hydraulic fluidthrough pipe 111. Helium is then pumped through line 112 until thepressure reaches 1200 bar g as measured by pressure gauge 117 at whichtime valve 113 is closed. A collector 118 is disposed circumjacent theoutside of the joint and is connected to a mass spectrometer 119 whichdraws in gas from the collector 118.

In conventional testing, once the helium has reached the test pressure,the joint 108 is left for 120 seconds and provided that no helium (orless than a specified amount of helium) is detected the joint is deemedacceptable.

The present invention differs in that immediately after the joint 108 ismade up an induction heater 114 is moved into place circumjacent thethreaded box 106 while the internal pressure tester 109 is beingpositioned and the seals 110 are activated.

The induction heater 114 is activated at the same time as valve 113 isopened to admit helium to the inside of the joint 108.

It is believed that the induction heater 114 heats the dope and lowersits viscosity, thus rendering it less capable of blocking a leak. Inaddition it is believed that any thermal expansion of the threaded box106 relative to the tubular 100 will help expose any latent defect.

Typically, the outside of the threaded box, 106 should be heated toabout 100° C. However, it is believed that the decrease in the viscosityof the dope consequent on heating is particularly important.

A useful advantage of the test procedure relates to pockets of air whichmay be trapped in the threads when the joint is made-up. In particular,such pockets of air can expand and distort a joint if it is subjected toa sufficiently high temperature down the wellbore. The test proceduredescribed enables many small bubbles to escape thus inhibiting problemsarising later.

The method of testing described with reference to FIG. 2 may also beused in a depot prior to dispatching new tubulars or refurbishedtubulars. It may also be used for testing joints when running tubularsdown a well.

FIG. 3 shows a method of testing which is generally similar to thatdescribed with reference to FIG. 2 except that the induction heater 114is replaced by a steam chamber 214 which is disposed circumjacent thethreaded box 206 and defined between the outer wall of the threaded box206, a cylindrical member 220 and seals 221 and 222 which projectinwardly from the cylindrical member 220 into sealing engagement withthe threaded box 206.

In use, after the internal pressure tester has been positioned as shownhelium is introduced into the inside of the threaded box 206.Simultaneously, superheated steam is introduced into the steam chamber214 via inlets 215. Air, condensate and some steam leave the steamchamber 214 via outlets 216. Should the joint fail helium will pass intoone or both the annular collectors 218 and will be sucked into a massspectrometer (not shown) via hoses 218'. It will be noted that one ofthe annular collectors 218 is defined between one end of the cylindricalmember 220, the seal 221 and a seal 223 which extends from thecylindrical member 220 to the outer wall of the tubular 207. The otherannular collector 218 is defined between the other end of thecylindrical member 220, the seal 222 and a seal 224 which extends fromthe cylindrical member 220 to the outer wall of the tubular 200.

The embodiment shown in FIG. 4 is generally similar to the embodimentshown in FIG. 3 except that the steam chamber 214 is provided with aperforated cylinder 225 to help distribute the superheated steam moreevenly over the circumference of the threaded box 206.

Referring now to FIG. 5 there is shown an external pressure tester whichis particularly useful for testing joints when running casing down awell.

In use a length of casing 300 is held by slips (not shown). The casing300 has an upwardly extending threaded pin 301 on which is mounted athreaded box 306. The threaded box 306 is normally mounted on the pin301 at the factory or depot.

The inside of the upper portion of the socket 306 is coated with dopeand the pin 302 of a tubular 307 is inserted therein. The joint 308 isthen tightened to the required torque by a tong (not shown).

The external pressure tester, which is generally identified by referencenumeral 309 is then applied to the joint 308. The external pressuretester is generally similar to that shown in U.S. Pat. No. 5,255,559except that it also includes an induction heater 314.

As soon as the external pressure tester 309 is clamped in position theinduction heater 314 is activated. Simultaneously, helium is introducedinto chambers 315 and 316 until the pressure reaches 1200 bar g asmeasured by pressure gauges 317 and 318 respectively. At this timevalves 319 and 320 are closed.

The intake of a gas detector (not shown) is disposed inside the tubular307 in the vicinity of the threaded box 306. If less than a specifiedamount of helium is detected in a given time the joint is deemedsatisfactory, the tubular lowered down the well and the processrepeated.

If the joint is found to be unacceptable it is either remade or replacedas required.

Laboratory experiments have been conducted by the Applicants withapparatus similar to that shown in FIGS. 1 and 2.

In particular, a small notch was cut in the seal area 103 of a 14 cm(51/2 inch) NEW VAM joint in order to simulate a defect. A small holewas then drilled into the box 106 and terminated at a positionimmediately adjacent the thread. A thermocouple was inserted in thesmall hole which was then packed with sealing wax.

Before each test the threaded pin 101 and threaded box 106 were cleanedthoroughly and a measured quantity of dope was applied evenly to thethreads of the threaded box 106 using a Weatherford "AccuKote" dopeapplicator. The connection was subsequently made up to the torque valuespecified by the pipe manufacturers using a computer controlled (JAM)makeup system in association with a Weatherford model 7.6 hydraulicpower tong with a free-floating backup.

An internal pressure tester 109 was inserted through the tubular 107 andpositioned as shown in FIG. 2. The seals 110 were urged radiallyoutwardly by introducing hydraulic fluid through line 112. Collector 118was disposed circumjacent the outside of the joint and was connected toa mass spectrometer 119 which drew in gas from the collector 118.

At the commencement of each test helium was admitted to the inside ofthe joint via line 112 and, simultaneously, power was applied to theinduction heater 114. Power was applied to the induction heater 114 forvarying lengths of time and the temperature at the thermocouple recordedwhen the power to the induction heater 114 was switched off.

The results of the tests were as follows:

    ______________________________________                                                                     Time to Test                                             Weight of                                                                              Temperature Detection of                                                                          Pressure                                 Test    Dope (g) (° C.)                                                                             Failure (s)                                                                           (bar g)                                  ______________________________________                                        1       10       26          5       400                                      2       20       80          45      400                                      3       70       26          120     400                                      4       70       26          180     400                                      5       70       90          20      400                                      6       70       100         3       200                                      7       80       26          300     400                                      8       80       60          25      400                                      9       80       80          50      400                                      ______________________________________                                    

The manufacturer's recommendations are that approximately 20 g of dopeshould be used on this type of joint. However, in practice, unless aspecial applicator is used field measurements suggest that fieldoperatives typically apply between 70 and 80 g of dope per joint. Forthis reason many of the tests were carried out with this quantity ofdope.

As can be seen, with minimal dope (Test 1) the defect became apparentvery rapidly at ambient temperature. However, with 70 g of dope, atambient temperature, the defect did not become apparent for 120 s (Test3) and 180 s (Test 4) respectively. Such a defect would probably havegone unnoticed in conventional commercial pressure testing whichtypically rarely exceeds two minutes. However, it will be noted thatwhen heating was applied to raise the temperature to 90° C. and 100° C.the defect became apparent in 20 and 3 seconds respectively (Test 5 and6).

Test 7 demonstrates how a generous (80 g) application of dope preventeddetection of the defect for 300 s at 80° C. However, when the joint washeated to 60° C. and 80° C. the defect was detected at 25 s and 50 srespectively (the latter result reflecting the degree of variationobserved).

Test 2 shows that with the correct amount of dope applied the defectwould have been detected in just 45 s at 80° C. From Test 6 it can bereasonably assumed that the time to detect the defect would besignificantly less at 100° C.

The results indicate that by selecting appropriate temperatures itshould be possible to detect defects which would probably have goneunobserved during conventional commercial pressure testing lasting 90 to120 s in under 45 s.

The laboratory tests indicate that, in the field, it should be possibleto routinely test 15 to 20 joints per hour when running casing andpossibly more with a good rig crew.

Various modifications to the embodiments described are envisaged. Forexample, liquid can be used as the test fluid. In this case leakage isdetected by noting a drop of pressure at the pressure gauges. Ifdesired, the induction heater 124 or the steam chamber 214 may comprisetwo parts which are hinged together and which can be mounted around ajoint.

I claim:
 1. A method for testing threaded joints and threaded members,the method comprisinglubricating with a lubricant one or both threadedmembers of two threaded members for forming a threaded joint, making upa threaded joint with the two threaded members, subjecting said threadedjoint to a pressure differential, and testing said joint by attemptingto detect flow through said joint, characterized in that said methodincludes the step of subjecting said joint to heat in order to reduceviscosity of said lubricant, and subjecting said joint to vibration atan ultrasonic frequency during said test, repeatedly carrying out saidmethod to at least 5 joints per hour.
 2. The method according to claim 1characterized in that said heat is applied during testing.
 3. The methodaccording to claim 1 characterized in that said heating is effected byinductance.
 4. The method according to claim 1 characterized in thatsaid heating is effected by steam.
 5. The method according to claim 1when carried out at a rate of at least 10 joints per hour.